A MULTILAYER METALLIZED FOSTED POLYPROPYLENE (CPP) FILM

Abstract

The present description relates to a multilayer film comprising: a) a metallizable skin layer comprising a polyolefin and antiblocking agent; b) a middle core layer comprising a homopolymer PP resin and a hardener; and c) a sealing layer comprising a copolymer and an antiblocking agent; said multilayer film has high metal bonding and high barrier properties and can be used in food packaging requiring very high metal bonding and high barrier to oxygen and moisture.

Description

A MULTILAYER METALLIZED FOSTED POLYPROPYLENE (CPP) FILM FIELD OF THE INVENTION This description refers to an adhesive film, and more specifically to a multilayer metallized cast polypropylene (CPP) film with high metal bonding and high barrier properties. This film can be used in food packaging. BACKGROUND OF THE INVENTION Commercially available metallized packaging films made of cast polyethylene (CPP) face problems of poor metal adhesion and bonding strength that limit their end-use applications. These metallized polyethylene films have polyethylene (PE) in the skin layer(s) that may contain low molecular weight PE fractions and high molecular weight comonomer fractions of linear low-density polyethylene (LLDPE). Such PE-based metallized films typically exhibit very poor bonding strength due to poor metal adhesion to the metallized skin layer, leading to changes during lamination, as well as poor barrier properties due to metal transfer. Existing metallized cast polyethylene (CPP) films used in food packaging have a metal bond strength between 60 and 80 g / 2.54 cm (inch). After lamination (with adhesive or extrusion) with biaxially oriented polypropylene (BOPP) or polyester (PET) films as the second substrate, due to the low adhesion of the metal layer to the metallized skin, the metal layer of the CPP film transfers to the other substrate (which may be BOPP or PET) along with the PE. This metal transfer also negatively affects the moisture barrier properties, resulting in a reduced shelf life of the packaged product. U.S. Patent 5,153,074 to Migliorini describes a metallized film combination comprising a polymer substrate with an ethylene vinyl alcohol copolymer skin layer and a thin metallic layer deposited on the surface of the ethylene vinyl alcohol copolymer. A maleic anhydride-modified propylene homopolymer or copolymer is provided for proper adhesion of the polyvinyl alcohol copolymer skin layer to the polymer substrate. The resulting metallized layer exhibits outstanding resistance to the transmission of oxygen or other gases. U.S. Patent 5,194,318 to Migliorini et al. describes a combination of ML / E / ZuZZ / u 1UOU is a metallized oriented film comprising a propylene polymer substrate with a high-density polyethylene skin layer and a thin metallic layer deposited on the high-density polyethylene surface. The resulting metallized film exhibits outstanding metallic adhesion to the polymer substrate and good moisture and oxygen barrier properties. U.S. Patent No. 5,591,520 to Migliorini et al. describes a metallized film combination comprising a propylene substrate with an amorphous polyamide skin layer and a thin metallic layer deposited on the surface of the amorphous polyamide skin layer. A metal anhydride-modified propylene homopolymer or copolymer is provided to bond the amorphous polyamide skin layer to the polymer substrate. The resulting metallized layer exhibits outstanding resistance to the transmission of oxygen and other gases. US20160144603A1 describes a multilayer structure comprising: (a) a skin layer comprising at least 50 wt% of an ethylene / alphaolefin interpolymer (LLDPE) composition having a comonomer distribution constant (CDC) in the range of 45 to 400, and wherein the skin layer does not contain any migratory additives; (b) a metallic layer disposed on the skin layer to form a metallized film; and (c) at least one substrate layer laminated onto the metallized film; wherein the ethylene / alphaolefin interpolymer composition comprises (i) less than or equal to 100 wt% of ethylene-derived units; and (ii) less than 30 wt% of units derived from one or more alphaolefin comonomers is provided. US patent publication US20160144603A1 mentions metallized polyethylene film.In US20160144603A1, the three layers—the sealant layer, core layers, and skin layer to be metallized—comprise LDPE and LLDPE. It also uses a processing aid (PPA). Furthermore, the existing patent US20160144603A1 mentions the film produced by a blown film extrusion process. None of the above techniques describe a multilayer metallized cast polypropylene (CPP) film that has both high metal-bonding strength and improved metal adhesion properties. Therefore, it would be desirable to produce multilayer metallized polypropylene films that have both high metal-bonding strength and improved metal adhesion properties. OBJECTIVES OF THE INVENTION One objective of the invention is to provide a multilayer metallized cast polypropylene (CPP) film with high metal bonding strength. Another objective of the invention is to provide a molten polypropylene film ML / E / ZuZZ / u 1UO» multilayer metallized (CPP) that improves oxygen and moisture barrier. BRIEF DESCRIPTION OF THE INVENTION In one aspect of the invention, a multilayer metallized cast polypropylene (CPP) film is provided, comprising: a) a metallizable skin layer comprising a polyolefin and an antiblock; b) a middle core layer comprising a homopolymer PP resin and a hardener; and c) a sealing layer comprising a copolymer and an antiblocking agent. In another aspect of the invention, a multilayer metallized cast polypropylene (CPP) film is provided that has high metal bonding strength and high oxygen and moisture barrier used in food packaging. These and other features, aspects, and advantages of this subject will be better understood with reference to the following description. This brief description is provided to introduce a selection of concepts in a simplified form. This brief description is not intended to identify key features or essential characteristics of the subject, nor is it intended to be used to limit the scope of the subject. BRIEF DESCRIPTION OF THE FIGURES The above characteristics, aspects, and advantages, and others related to the subject matter, will be better understood with respect to the following description and accompanying figures, where: Figure 1 is a schematic illustrating the multilayer metallized cast polypropylene (CPP) film of the present description. Figure 2 is a schematic illustrating one modality of the multilayer metallized cast polypropylene (CPP) film of the present description. Figure 3 is a schematic illustrating another form of the multilayer metallized cast polypropylene (CPP) film described herein. DETAILED DESCRIPTION OF THE INVENTION For convenience, the terms used herein have the meanings recognized and known by those technically skilled in the field; however, for convenience and integrity, particular terms and their meanings are set out below. ML / E / ZuZz / u 1UO» The articles a, one, and the are used to refer to one or more of one (i.e., at least one) of the grammatical object of the article. The terms include and that includes are used in the inclusive, open sense, meaning that additional elements may be included. They are not intended to be interpreted as consisting solely of. Throughout the description, unless the context otherwise requires, the word include, and variations such as includes and that includes, will be understood to imply the inclusion of a mentioned element or step or group of elements or steps, but not the exclusion of any other element or step or group of elements or steps. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by a person skilled in the art to whom this description pertains. Although any methods and materials similar to or equivalent to those described herein may be used in the practice or testing of the description, the preferred methods and materials are described herein. All publications mentioned herein are incorporated by reference. The present description is a multi-layer metallized cast polypropylene (CPP) film with high metal bonding strength and high metal bonding and barrier properties. The multilayer metallized cast polypropylene (CPP) film, in accordance with the present description, comprises: a) a metallized skin layer comprising a polyolefin and an anti-blocking agent; b) a middle core layer comprising a homopolymer PP resin and a hardener; and c) a sealing layer comprising a copolymer and an antiblocking agent. In one embodiment of the invention, the multilayer metallized cast polypropylene (CPP) film comprises an adhesive layer applied over the metallizable skin layer and the film laminated with a substrate. In another embodiment of the invention, the multilayer metallized cast polypropylene (CPP) film comprises an extrusion resin layer applied over the metallizable skin layer and the film laminated with a substrate. In another embodiment of the invention, the substrate is selected from the group comprising PP, PET, BOPP or any thermoplastic flexible packaging film or combination thereof. In another embodiment of the invention, the polyolefin is selected from a group consisting of LLDPE, mLLDPE, and HDPE, or a combination thereof. Furthermore, the LLDPE is in the ML / E / ZυZZZ / υΊ 1UOU range of 5 to 94% by weight, mLLDPE is in the range of 5 to 94%, HDPE is in the range of 90 to 95%. In another embodiment of the invention, the antiblocking agent in the metallizable skin layer is in the range of 1 to 35%. The antiblocking agent is selected from the group consisting of synthetic silica, limestone, natural silica, talc, zeolites, organic additives, etc. In another embodiment of the invention, the homopolymer PP resin is present in the range of 100% by weight. In another embodiment of the invention, the hardener is present in the range of 5 to 30% by weight. The hardener is selected from the group consisting of Cs- to C9-based polymers. In another embodiment of the invention, the copolymer is in the range of 90 to 98% by weight. The copolymer is selected from the group consisting of ethylene-propylene copolymers produced using Ziegler-Natta catalysts or ethylene-propylene copolymers produced using metallocene catalysts or ethylene-propylene-butylene terpolymers. In another embodiment of the invention, the antiblocking agent in the sealing layer is present in the range of 2 to 10% by weight. The antiblocking agent in the sealing layer is selected from the group consisting of synthetic silica, limestone, natural silica, talc, zeolites, organic additives, etc. In another embodiment of the invention, the metallizable skin layer has a thickness in the range of 4 to 35% of the total film thickness. In a preferred embodiment of the invention, the skin layer has a thickness in the range of 5 to 20% of the total film thickness. In another embodiment of the invention, the core layer has a thickness in the range of 40 to 80% of the total film thickness. In another embodiment of the invention, the sealing layer has a thickness in the range of 10 to 40% of the total film thickness. In another embodiment of the invention, the additive is selected from the group consisting of solvent-based additives and solvent-based additives, or a combination thereof. The solvent-based additives are selected from the group consisting of acrylics, polyesters, and other food-grade adhesives. The solvent-based additives are selected from the group consisting of water-based adhesives formulated from dextrins, sodium silicates, natural rubbers, vinyl acetate-based emulsions, acrylic, and polyurethane. Polyurethane dispersions of anionic polyester and aliphatic isocyanates are also included. Crosslinkers for polyurethane dispersions may be polyazirides, polyisocyanates, carbodiimides, epoxies and epoxy silanes, vinyl acetate, and acrylic copolymers. Solvent-free adhesives comprising one-part and two-part polyurethanes are also included. In another embodiment of the invention, the surface of the metallizable skin layer is ML / E / ZuZZ / u1UO» is treated using corona discharge, plasma treatment, or flame treatment methods. A thin layer of metal is deposited under vacuum onto the metallizable skin layer during the metallization process. This metal layer can be any metal, but preferably a thin layer of aluminum. The metallized film is laminated onto the substrate by adhesive lamination or extrusion lamination. The metal-bonding strength of the multilayer film described herein is greater than 250 g / 2.57 cm (inch). Due to such high metal-bonding strength values, the adhesion of the metal layer to the metallized skin is such that no metal transfer is observed after extrusion, thus improving or maintaining the moisture and oxygen barrier. Because of these attributes, the multilayer film described herein is suitable for all lamination techniques. The multilayer film in accordance with various modalities of the present description may be in the form of a bag or a food packaging film. EXAMPLES The following examples are provided for illustrative purposes only and should not be interpreted as limiting the scope of this description. Both the preceding general description and the following detailed description are understood to be illustrative and explanatory only and are intended to provide further explanation of the subject matter. EXAMPLE 1 A three-layer film, having a metallizable skin layer, a middle core layer, and a sealing layer with properties shown in Table 2 below, was prepared. Table 1 below provides the composition for each of the three layers: ML / E / ZuZz / u 1UO» TABLE 1 Components of a three-layer film Film Layer Component Percentage Thickness Treated Metallizable Layer • LLDPE (MFI range 0.8 to 10 g / 10 min; density 0.91 to 0.94 g / cm3) • mLLDPE (MFI range 0.8 to 10 g / 10 min; density 0.91 to 0.900) 36 55 to 94% 5-35% 4 to 35% g / cm3) • Antiblocking agent in PP carrier (organic or inorganic additive with additive loading between 2% and 25%) 1-10% Core layer • 100% homopolymer PP 40 to 80% Sealing layer • Copolymer with seal start temperature 80 to 125 °C • Antiblocking agent in PP carrier (organic or inorganic additive with additive loading between 2% and 25%) 90 to 98% 2 to 10% 10 to 40% ML / E / ZuZz / u luoy TABLE 2 Properties of a three-layer film Criteria Optical density 1.8 to 3.0 Metal bonding strength > 300 grams / 2.54 cm (inch) MVTR < 1.0g / m2-day OTR <125 cc / m2-day EXAMPLE 2 A three-layer film, comprising a metallizable skin layer, a middle core layer, and a sealing layer with properties shown in Table 4 below, was prepared. Table 3 below provides the composition for each of the three layers: TABLE 3 Components of a three-layer film Film Layer Component Percentage Thickness Treated Metallizable Layer • LLDPE (MFI range 0.8 to 10 g / 10 min; density 0.91 to 0.94 g / cm3) • mLLDPE (MFI range 0.8 to 10 g / 10 min; density 5 to 35% 94 to 55% 4 to 35% 0.91 to 0.900 36 g / cm3) • Antiblocking agent in PE or PP carrier (organic or inorganic additive with additive loading between 2% and 25%) 1 to 10% Core layer. 100% homopolymer PP 40 to 80% Sealing layer • Copolymer with seal start temperature 80 to 125 °C • Antiblocking agent in PP carrier (organic or inorganic additive with additive loading between 2% and 25%) 90 to 98% 2 to 10% 10 to 40% ML / E / ZuZz / u 1UO» TABLE 4 Properties of a three-layer film Criteria Optical density 1.8 to 3.0 Metal bonding strength > 300 qram / 2.54 cm (in) MVTR < 1 q / m2-day OTR <125 cc / m2-day EXAMPLE 3 A three-layer film, having a metallizable skin layer, a middle core layer, and a sealing layer with properties shown in Table 6 below, was prepared. Table 5 below provides the composition for each of the three layers: TABLE 5 Components of a three-layer film Film Layer Component Percentage Thickness Treated Metallizable Layer • HDPE (MFI range 0.8 to 10 g / 10 min; density 0.94 to 0.965 g / cm3) • Antiblocking on PE or PP carrier (organic or inorganic additive with the 90 to 95% 5 to 35% 4 to 35% Additive loading between 2% and 25%) Core layer. 100% homopolymer PP 40 to 80% Sealing layer • Copolymer with seal start temperature 80 to 125 °C • Antiblocking on PP carrier (organic or inorganic additive with additive loading between 2% and 25% 90 to 98% 2 to 10% 10 to 40% IVIA / t / ZUZZ / UI lUOU TABLE 6 Properties of a three-layer film Criteria Optical density 1.8 to 3.0 Metal bonding strength > 250 grams / 2.54 cm (inch) MVTR < 0.3 g / m2-day OTR < 30 cc / m2-day EXAMPLE 4 COMPARATIVE EXAMPLE The following example illustrates that the multilayer metallized cast polypropylene (CPP) film of the present invention has better metal bonding strength compared to 10 existing metallized CPP films. Existing Metallized CPP Structure Metallized CPP of the Present Application Bonding Strength (grams / 2.54 cm (inch)) Bonding Strength (grams / 2.54 cm (inch)) Extrusion PE to Metallized CPP 30 to 47 140 to 175 Bonding Strength to Metal per AIMCAL TP-105-92 60 to 80 More than 300 EXAMPLE 5 BOND STRENGTH CALCULATION Adhesion to metal or other metal-to-metal bonding strength is calculated using EAA seal and peel test (AIMCAL TP-105-92) The metallizable skin of the present invention comprises a blend of m-LLDPE and LLDPE as opposed to the PP-based polymers used in existing metallized CPP films. This novel skin composition provides high bonding / adhesion to metal. Hardeners used in the core layer help improve the moisture and oxygen barrier. These characteristics are absent in existing films. Advantage of the Invention High metal bonding of the cast or metallized multilayer polypropylene (CPP) film of the present description prevents transfer or removal of metal from the metallized skin layer that helps retain the oxygen and moisture barrier, thereby extending the shelf life of products. Industrial use / function / application The multilayer metallized cast polypropylene (CPP) film described herein can be used in food packaging that requires very high metal bonding and a high barrier to oxygen and moisture. For example: packaging bakery products, spices, snacks, etc. The multilayer metallized cast polypropylene (CPP) film described herein is not limited to the embodiments discussed and may be represented by various modifications within the scope of the following claims. It should be recognized that the preferred embodiments described above are merely illustrative. Certain modifications and improvements will occur to the person skilled in the art after reading the preceding description. It is understood that all such modifications and improvements have been omitted here for the sake of brevity and readability but are appropriately within the scope of the following claims.

Claims

1. A multilayer metallized melt-polypropylene (CPP) film comprising: a) a metallizable PE skin layer comprising a polyolefin and an antiblocking agent; b) a middle core layer comprising a homopolymer PP resin and a hardener; and c) a sealing layer comprising a copolymer and an antiblocking agent.

2. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the multilayer film comprises an adhesive layer applied over the metallizable skin layer.

3. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the multilayer film comprises an extrusion resin layer applied over the metallizable skin layer.

4. The multilayer metallized cast polypropylene (CPP) film according to any of claims 2 and 3, further characterized in that the multilayer film is laminated with a substrate.

5. The multilayer metallized cast polypropylene (CPP) film according to claim 4, further characterized in that the substrate consists of PP, PET, BOPP or thermoplastic flexible packaging film.

6. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the polyolefin is selected from a group consisting of LLDPE, mLLDPE, and HDPE or a combination thereof.

7. The multilayer metallized cast polypropylene (CPP) film according to claim 6, further characterized in that the LLDPE is in the range of 5 to 94%.

8. The multilayer metallized cast polypropylene (CPP) film according to claim 6, further characterized in that the mLLDPE is in the range of 5 to 94%.

9. The multilayer metallized cast polypropylene (CPP) film according to claim 6, further characterized in that the HDP is in the range of 90 to 95%.

10. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the antiblocking in the metallizable skin layer is in the range of 1 to 35%.

11. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the homopolymer PP resin is present in the range of 100% by weight.

12. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the hardener is present in the range of 5 to 30% by weight.

13. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the copolymer is in the range of 90 to 98% by weight.

14. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the antiblocking agent in the sealing layer is present in the range of 2 to 10% by weight.

15. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the metallizable skin layer has a thickness in the range of 4 to 35% of the total film thickness.

16. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the core layer has a thickness in the range of 40 to 80% of the total film thickness.

17. The multilayer metallized cast polypropylene (CPP) film according to claim 1, further characterized in that the sealing layer has a thickness in the range of 10 to 40% of the total film thickness.

18. The multilayer metallized cast polypropylene (CPP) film according to claim 2, further characterized in that the additive is selected from the group consisting of solvent-based additives and non-solvent-based additives or combinations thereof.